Method of cladding



y 21, 1964 B. B. DUNNE ETAL METHOD OF CLADDING 2 Sheets-Sheet 1 FiledJune 1, 1960 .005 Climfg m m 7 mm? m MWZ 3B4, NVOm p w 50W 6?. {as

y 21, 1964 B. B. DUNNE ETAL METHOD OF CLADDING 2 Sheets-Sheet 2 FiledJune 1. 1960 By PZ/F/PVB 7F/77Z WON/41D H KEZSfy S OMS andvbsm a oeals3,141,236 NETHOD OF CLADDING Brian B. Dunne, San Diego, Perry E. Ritter,Encinitas,

and Ronald A. Kelsey, Del Mar, Califi, assignors to General DynamicsCorporation, New York, N.Y., a

corporation of Delaware Filed June 1, 1960, Ser. No. 33,133 3 Claims.(Cl. 29421) This invention relates to a method of cladding which is ofparticular value for applying coverings of metal or other similarmaterials to objects of irregular shape or of non-uniform cross section.

In the application of thin protective metallic sleeves or jackets, incertain cases, it is not possible to employ a rolling, swaging orextrusion process. This is particularly true in the case of an elementof such character that it is either not feasible to use an extrusionprocess because of the nature of the product, or where the element isirregular in shape or has circumferential grooves or other indentations.

The object of this invention is to provide a convenient, economical andefficient method of applying a protective jacket or other relativelythin metal covering to an object made of a rigid material such as metal,for example, a fuel rod of irregular cross section such as may be usedin nuclear reactor.

A further object of the invention is to provide a cladding method as anincident to which method there is evacuated from the interior of thesleeve any air or other gas which might be present in or about theobject in such amounts as might interfere with the efficient prac ticeof the method, or which might later interfere with the use of thefinished product.

Other more specific objects and advantages of the invention will bedisclosed as the description proceeds.

In general, it may be said that these objects and results are effectedby detonating an explosive charge within liquid in which there has beenimmersed the rigid metal object around which has been placed a jacket ofdeformable material such as loosely fitting metal sleeve. When theexplosive is detonated, the pressure created within the liquid adjacentthe jacketed object will almost instantaneously cause the jacket to beforced into intimate engagement with the exterior of the rigid object.To avoid air pockets between the jacket and the metal object, the spacebetween the metal object and the jacket is preferably evacuated prior tothe detonation of the explosive.

The drawings which accompany this specification illustrate an embodimentof the invention which has successfully been employed in the cladding ofnuclear reactor fuel rods, the exterior surfaces of which have exteriorindentations, for example, in the present instance, circumferentialgrooves or recesses.

FIGURE 1 of the drawings represents a side view of a partial verticalsection through a tank in which the fuel rod with its prospective shieldhas been assembled in a treatment tank before detonating the explosive;

FIGURE 2 is a plan view of the set-up shown in FIG- URE 1, partly insection, and taken through the line 2-2 of FIGURE 1; and

FIGURE 3 is a side elevation, partly in section, of the jacketed fuelrod after the cladding has been applied and the ends of the claddingsleeve have been scaled by insertion of the upper and lower heads.

Referring to the drawings, which disclose the invention as applied tothe cladding of a nuclear reactor fuel rod, the fuel or meat of the rodis represented by the numeral 10 which, as shown in FIGURE 1, isprovided with a series of circumferentially extending grooves 11. Exceptfor the said grooves 11, the fuel rod 10 is in United States Patent "icethe form of a cylinder which may be two or more feet in length and oneand one-half inches or more in diameter. The sleeve or jacket 12 whichcan be of aluminum or other appropriate metal, has a wall thickness ofabout .030 inch, and has an interior diameter about 0.003 inch greaterthan that of the rod 10 so that it will loosely fit the exterior of therod 10 whereby said core rod 10 may be easily slipped into the sleeve12, as shown in FIG- URE 1.

For the purpose of evacuating any gas, such as air, which may becontained within the grooves 11 or elsewhere in the assembled orjacketed rod, the ends of the sleeve 12 are sealed. This may be done bymeans of a pair of end plates or discs 13 and 14 made of lucite or othersuitable material. Each of these end plates is made with an internalcircumferentially extending groove 15, preferably rectangular in crosssection, and fitted at its inner end with an O-ring 16 or similar gasketserving as a seal to prevent air or other gas from leaking back.

into the assembly after it has been evacuated. Such evacuation may beeffected through a small pipe 17 in the upper lucite cover plate 13. Itis not generally necessary to evacuate the assembly to a very lowpressure. Evacuation to a level of the order of 1 mm. of mercury(absolute pressure) will ordinarily be sufiicient.

The evacuated assembly with the sealing caps 13 and 14 still in place isnow placed in a tank of water large enough so as to avoid distortions inthe inwardly directed pressure waves which are subsequently formed inthe water. In the case of a rod one and one-half inches in diameter, theassembly should be completely surrounded by at least about twelve inchesof water.

Before the sealed and evacuated assembly is lowered into the tank ofwater, a pair of thin discs 18 and 19 are secured to the outer surfacesof the plates 13 and 14. These serve to position the explosive chargewhich, in the present instance, comprises a plurality of, preferablythree or more, vertically extending, generally parallel cords 20, 21 and22, the upper ends of which are tied or otherwise brought together atthe firing point 23. In the case of a rod one and one-half inches indiameter, and where three explosive cords are used, these cords may belocated in a cylindrical zone and about one inch from the sleeve orjacket 12, the cords being equally spaced around the axis and positionedat an angle of as shown in FIGURE 2.

The explosive cords are formed of an explosive which preferably has arelatively high detonation velocity, for example, such as that which ismarketed by The Du Pont Company under the name Primacord and containsPETN (pentaerithritoltetranitrate). In the present case, it may have anoutside diameter of about onequarter inch and contain about thirtygrains of PETN per foot. It has been found that when this explosive cordis detonated at the firing point 23, the explosion will be propagatedsimultaneously at the same rate through each of the three explosivecords, and since the three cords are symmetrically positioned around theaxis of the rod and of equal length, the shock waves from the threecords will be at the same level and the combined shock wave will travelprogressively downward from the disc 18 to the disc 19. This willproduce a sudden hydraulic pressure, around the jacketed rod, of aboutthree to four kilobars above the yield point of the aluminum sleeve 12,causing it to flow plastically.

In view of the fact that the shock wave will travel down the Primacordcords at an extremely high velocity (about 6000 meters per second)whereas the propagation velocity through water is only about 1500 metersper second, the pressure around the sleeve will be well distributed andconcentrated around the circumference of the outside of the sleeve withthe result that the sleeve contracted onto the object.

n) will be forced into close fitting intimate engagement with the rod Asa result, the sleeve will be forced tightly into intimate contact withthe rod 10 progressively threuLgrhout its entire length of two feet ormore.

After the explosion has been effected, the assembly may be removed fromthe tank. To form the fuel element shown in FIGURE 3, seals, preferablyof the same metal as the sleeve 12, aluminum in this case, are thenapplied and welded in place in the ends of the sleeve, as

jshown in FIGURE'3, Where 25 represents the seal at the upper end of therod and 26 represents the seal at the lower end of the rod.

v In some instances, particularly when the object which is to be clad isof generally nniformpcross section, the air in the space between theobject and the cladding may The expelleclby the progressive downwardpassage of the shock wave which will force the air between the rod andcladding to move downwardly as the cladding is In such a case, the priorevacuation of the air from the assembly will not be necessary.

' The method of cladding described above has been used to successfullyclad objects of various shapes, including cruciform shaped rods,hexagonal rods, rods of rectangular cross section, rods provided withspiral grooves, rods provided with elongated fins, etc. It should beunderstood that the optimum number of explosive cords and the path ofthe cords relative to the object being clad will depend upon thespecific shape of the object being clad. If the plurality of Primacordelements is such that they are adjacent, or nearly adjacent to oneanother,

they may be conveniently replaced by a thin sheet of 'or a sheet of theexplosive material, one may use a single co-axial strand of theexplosive material or a sheet of the explosive formed into a tubularshape.

Various of the features of the present invention believed to be new areset forth in theappended claims.

What is claimed is:

1. A method of applying a tight-fitting layer of metal to a rigidelongated core, which comprises inserting the core in a loose fittingjacket of malleable metal, evacuating the space defined between the coreand the jacket, immersing the jacketed core in a liquid, providing aplurality of elongated bodies of an explosive substance which,are spacedfrom and which extend generally parallel to the jacketed core and whichare positioned in generally equi-spaced relationship around the jacketedcore, and simultaneously detonating said elongated bodies of explosivesubstance from the same ends to thereby provide a generally uniformshock wave in the liquid which extends around the jacketed core andwhich travels progressively along the length of the jacketed core toprogressively contract the jacket into generally intimate contact withthe core; L p n v 2. A method of applying a tight-fitting layer of metalto a rigid elongated rod, which comprises inserting the rod in a loosejacket of malleable metal, placing the jacketed rod in a tank of liquid,providing at least three explosive cords which are spaced from and whichextend generally parallel to the jacketed rod and which are positionedin generally equi-spaced relationship around the jacketed rod, andsimultaneously detonating said explosive cords from the same ends tothereby. provide a generally uniform shock wave in the liquid whichextends around the jacketed rod and which travels progressively alongthe length of the jacketed rod to progressively contract the jacket intogenerally intimate contact with the rod while simultaneously exuding airfrom the space between the jacket and the rod.

3. A method of applying a tight-fitting layer of metal to a rigidelongated rod, which comprises inserting the vrod in a loose fittingjacket of malleable metal, evacuating the space defined between the rodand the jacket, placing the jacketed rod in a tank of liquid, providingat least three explosive cords which extend from a cornmon detonatingpoint and which are spaced from and extend generally parallel to thejacketed rod and which are positioned in generally equi-spacedrelationship around the jacketed rod, said explosiveco'rds extendingalong the entire length of the rod, and simultaneously detonating saidexplosive cords from said common detonating point to thereby provide auniform shock wave in the liquid which extends, around the jacketed rodandrwhich travels progressively along the length of the jacketed rod toprogressively contract the jacket into generally intimate contact withthe rod.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Explosives Form Space Age Shapes, Steel, Aug. 25, 1958, pages82-86.

Explosive Forming, American Machinist, June 15, 1959, vol. 103, No. 12,pages 127-138.

1. A METHOD OF APPLYING A TIGHT-FITTING LAYER OF METAL TO A RIGIDELONGATED CORE, WHICH COMPRISES INSERTING THE CORE IN A LOOSE FITTINGJACKET OF MALLEABLE METAL, EVACUATING THE SPACE DEFINED BETWEEN THE COREAND THE JACKET, IMMERSING THE JACKETED CORE IN A LIQUID, PROVIDING APLURALITY OF ELONGATED BODIES OF AN EXPLOSIVE SUBSTANCE WHICH ARE SPACEDFROM AND WHICH EXTEND GENERALLY PARALLEL TO THE JACKETED CORE AND WHICHARE POSITIONED IN GENERALLY EQUI-SPACED RELATIONSHIP AROUND THE JACKETEDCORE, AND SIMU-SPACED RELATIONSHIP AROUND THE JACKETED CORE, ANDSIMULTANEOUSLY DETONATING SAID ELONGATED BODIES OF EXPLOSIVE SUBSTANCEFROM THE SAME ENDS TO THEREBY PROVIDE A GENERALLY UNIFORM SHOCK WAVE INTHE LIQUID WHICH EXTENDS AROUND THE JACKETED CORE AND WHICH TRAVELSPROGRESSIVELY ALONG THE LENGTH OF THE JACKETED CORE TO PROGRESSIVELYCONTRACT THE JACKET INTO GENERALLY INTIMATE CONTACT WITH THE CORE.